DESCRIPTION: (Adapted from the applicants abstract) There is growing concern about the number of critically ill patients requiring prolonged mechanical ventilatory support (MVS). Past research has focused on the use of point-in-time respiratory and ventilatory measures to predict a patient's success of breathing spontaneously. One area that has received little attention in these patients is cardiac function and the role it could play in preventing successful weaning from MVS. The purposes of this study are (1) to determine the relationship between left ventricular (LV) function and the duration of MVS, and (2) to validate hemodynamic categories with biochemical and physiologic response indicators of LV function. A secondary purpose is to describe the pharmacologic treatment of patients with compromised and severely compromised left ventricular function. The specific aims for this study are: 1. To determine if a relationship exists between LV function categorized by hemodynamic parameters (normal, compromised, and severely compromised) on Days 1 and 8 and the duration of MVS when controlling for nutritional status and spontaneous breathing pattern in mechanically ventilated adults. 2. To determine if a relationship exists between LV function categorized by hemodynamic parameters and biochemical indicator (plasma norepinephrine) levels and physiologic response indicators (arterial pressure response waveform during Valsalva maneuver) in mechanically ventilated subjects on days 1 and 8 of MVS 3. To determine what combinations of drugs are used to treat mechanically ventilated patients with compromised and severely compromised LV function. A prospective purposive sample of 46 subjects will be obtained from the population of patients who: are 18 years of age or older, are mechanically ventilated, had MVS initiated during this hospitalization, have an arterial pH between 7.35 and 7.45, and have a pulmonary artery catheter in place. The independent variable is LV function as measured by hemodynamic parameters (pulmonary artery occluded pressure), biochemical indicators (plasma norepinephrine levels), and physiologic response indicators (arterial waveform pattern during Valsalva). The moderating variables are breathing pattern, and nutritional status. The dependent variable is duration of MVS (days).